Protein chemistry and peptide synthesis have been a prominent feature of the Program's activities since its inception in 1968. Originally, these were carried out as a part of a component Project aimed at the structural analysis and study of the structure-activity relations of parathyroid hormone and calcitonin. Besides the earliest active synthetic calcium-regulating peptides, fundamental and enduring contributions to sequencing and synthetic methodologies emerged from these investigations. The increasing versatility of these chemical methods brought steadily expanding benefits to all of the projects;to meet the resulting needs, a separate Core was established in 1979. In addition to continued development of synthetic PTH agonists and antagonists, the Core proceeded to fulfill such diverse roles as identifying products of in vivo PTH metabolism, calibrating standards for a range of biological and immunological assays, characterizing and microsequencing recombinant expression products and biosynthetically labeled proteins, and characterizing membrane proteins in conjunction with the successful effort to purify the PTH/PTHrP receptor. With the move of the Endocrine Unit into the Wellman (now Their) Building laboratory in the mid-1980's came the first step in the process of resource sharing that continues to this day to bring major benefits to both the Program and the NIH. By formally consolidating in 1993 into a common analytical-synthesis facility with the Molecular Endocrinology and Reproductive Endocrine Units, followed by the Partners AIDS Research Center, the Core gained important new capabilities including gas-phase sequencing, microbore HPLC and enhanced synthesis capacity. Then, as now, operating costs were carefully allocated among the individual projects and investigators according to utilization, but the benefits realized from widened access to methodology, depth of experience, flexibility in personnel deployment and economies of scale were clearly apparent at the time of the last Program Project renewal.